N.Z. Zoned For Earthquake Risk

Press, Volume CII, Issue 30143, 29 May 1963, Page 10

N.Z. Zoned For Earthquake Risk

A division of New Zealand into areas of varying earthquake risk is made in a report to the Royal Society of New Zealand by members of its earthquake risk subcommittee. The division, worked out by four geologists and a geophysicist, is questioned by another geophysicist, who in a minority statement included in the report says that no area of New Zealand is sufficiently free from earthquake risk for zoning to be possible.

Christchurch, according to the majority statement, is included in the zone where destruction by earthquake is probable at several places in any period of a few hundred years, while damage is to be expected at numerous places in the same period. The majority statement—by Professor R. H. Clark, of the geology department, Victoria University of Wellington; Mr H. E. Fyfe, Mr G. J. Lensen, and Dr. R. P. Suggate, all of the Geological Survey, Department of Scientific and Industrial Research: and Mr R. R. Dibble, of the Seismological Observatory. D.S.l.R.—uses as a basis of its division the occurrence of destructive earthquakes in the (geologically speaking) recent or fairly recent past, the earthquakes being deduced on the evidence of geological warping and faults.

Forecast Not Possible “It must be stressed that it is not possible to forecast how soon or where the next destruction or damage will occur in any zone,” the statement warns.

Zone 1, the area in which the five scientists believe destructive earthquakes are most likely, covers the east and south of the North Island and practically all the north and west of the South Island. It includes the cities of Wellington. Gisborne, Napier, Hastings. Palmerston North.

and Nelson, with Wanganui indeterminate between zones 1 and 2. According to the authors, "destruction is probable in several parts of the zone in any period of 100 years. Damage is to be expected in numerous places in any period of tens of years ’’ Zone 2. the region next most severely at risk, comprises the rest of the South Island and a belt of the North Island including New Plymouth, Rotorua, Tauranga, and (on the borderline) Hamilton. In this area, “destruction is probable in several parts of the zone in any period of a few hundred years. Damage is to be expected at numerous places in any period of a few hundred years.” Zone 3 is confined, as far as land area is concerned, to Auckland city and its surrounding district. There is another belt of the zone off the east coast of the South Island, however, from Banks Peninsula south. "Destruction is possible, though not probable, in several parts of tire zone in any period of a few hundred years,” the authors say.

Zone 4 comprises the remainder of Northland, including Whangatei. The risk in this area is less than in the Auckland region. Dissenting View

i .The minority statement is iby Dr. F. F. Evison, of the j Seismological Observatory.- He I bases a proposed division on : the distance of any particular place from the epicentre of a recorded earthquake, and on this bases concludes that all New Zealand, except possibly the extreme tip of Northland, is in a region where earthquakes of damaging intensity may be expected at some time in the future. The convener of the committee. Mr R. W. Willett, of the Geological Survey, concludes that whether or not it is possible to make a division of the country into zones of greater or less earthquake risk, the risk is real in all areas. “Therefore,” he says there should be no relaxation of (building) codes or standards whatever. Any alteration of standards should be to raise them in these areas! that are known historically to] be subject to more earth-] quakes.”